The present invention relates, in general, to electronics, and more particularly, to methods of forming semiconductor devices and structure.
In the past, the semiconductor industry utilized various methods and structures to implement skip cycle detection and output power overload detection in switching power supply systems such as pulse width modulated (PWM) systems. Skip cycle detection, often referred to as burst-mode detection, was often used to reduce power dissipation in the power supply system during light output load conditions. Power overload detection was used to determine if the amount of output power supplied by the system was greater than the desired maximum power dissipation that was allowable by the particular implementation of the power supply system. One example of a switching power supply controller that had both power overload detection and skip cycle detection was the NCP1231 supplied by ON Semiconductor of Phoenix, Ariz.
Output power overload detection methods generally compared the value of a signal representative of the output voltage formed by the power supply system to a fixed reference voltage within the power supply controller. One problem with this method was that the output power delivered to the load could also increase if the value of the bulk input voltage supplied to the power supply system changed. In such a situation, the power supply controller of the power supply system could not accurately detect the power overload condition.
Skip cycle detection circuits also generally compared a signal representative of the value of the output voltage to a fixed reference voltage within the power supply controller. If the value of the bulk input voltage supplied to the power supply system changed, the skip cycle detection method could cause the power supply system to enter the skip cycle mode before the power required by the load decreased to the desired value. Consequently, the power supply system would not supply enough power to the load.
Accordingly, it is desirable to have a power supply control system and method that more accurately detects the power supplied by the power supply control system, that accurately detects the power supplied by the power supply control system when the bulk input voltage changes, and that more accurately detects the load power at which to enter the skip cycle mode.
For simplicity and clarity of illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or anode of a diode, and a control electrode means an element of the device that controls current through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain N-channel or P-Channel devices, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with the present invention. It will be appreciated by those skilled in the art that the words during, while, and when as used herein are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay between the reaction that is initiated by the initial action.